23.08.2019 17:37, Eric Blake wrote:
> Commit fe0480d6 and friends added BDRV_REQ_NO_FALLBACK as a way to
> avoid wasting time on a preliminary write-zero request that will later
> be rewritten by actual data, if it is known that the write-zero
> request will use a slow fallback; but in doing so, could not optimize
> for NBD. The NBD specification is now considering an extension that
> will allow passing on those semantics; this patch updates the new
> protocol bits and 'qemu-nbd --list' output to recognize the bit, as
> well as the new errno value possible when using the new flag; while
> upcoming patches will improve the client to use the feature when
> present, and the server to advertise support for it.
>
> Signed-off-by: Eric Blake <ebl...@redhat.com>
> ---
> docs/interop/nbd.txt | 3 ++-
> include/block/nbd.h | 4 ++++
> nbd/common.c | 5 +++++
> nbd/server.c | 2 ++
> qemu-nbd.c | 1 +
> 5 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt
> index 6dfec7f47647..45118809618e 100644
> --- a/docs/interop/nbd.txt
> +++ b/docs/interop/nbd.txt
> @@ -53,4 +53,5 @@ the operation of that feature.
> * 2.12: NBD_CMD_BLOCK_STATUS for "base:allocation"
> * 3.0: NBD_OPT_STARTTLS with TLS Pre-Shared Keys (PSK),
> NBD_CMD_BLOCK_STATUS for "qemu:dirty-bitmap:", NBD_CMD_CACHE
> -* 4.2: NBD_FLAG_CAN_MULTI_CONN for sharable read-only exports
> +* 4.2: NBD_FLAG_CAN_MULTI_CONN for sharable read-only exports,
> +NBD_CMD_FLAG_FAST_ZERO
> diff --git a/include/block/nbd.h b/include/block/nbd.h
> index 2c87b42dfd48..21550747cf35 100644
> --- a/include/block/nbd.h
> +++ b/include/block/nbd.h
> @@ -140,6 +140,7 @@ enum {
> NBD_FLAG_CAN_MULTI_CONN_BIT = 8, /* Multi-client cache consistent
> */
> NBD_FLAG_SEND_RESIZE_BIT = 9, /* Send resize */
> NBD_FLAG_SEND_CACHE_BIT = 10, /* Send CACHE (prefetch) */
> + NBD_FLAG_SEND_FAST_ZERO_BIT = 11, /* FAST_ZERO flag for WRITE_ZEROES
> */
> };
>
> #define NBD_FLAG_HAS_FLAGS (1 << NBD_FLAG_HAS_FLAGS_BIT)
> @@ -153,6 +154,7 @@ enum {
> #define NBD_FLAG_CAN_MULTI_CONN (1 << NBD_FLAG_CAN_MULTI_CONN_BIT)
> #define NBD_FLAG_SEND_RESIZE (1 << NBD_FLAG_SEND_RESIZE_BIT)
> #define NBD_FLAG_SEND_CACHE (1 << NBD_FLAG_SEND_CACHE_BIT)
> +#define NBD_FLAG_SEND_FAST_ZERO (1 << NBD_FLAG_SEND_FAST_ZERO_BIT)
>
> /* New-style handshake (global) flags, sent from server to client, and
> control what will happen during handshake phase. */
> @@ -205,6 +207,7 @@ enum {
> #define NBD_CMD_FLAG_DF (1 << 2) /* don't fragment structured read
> */
> #define NBD_CMD_FLAG_REQ_ONE (1 << 3) /* only one extent in BLOCK_STATUS
> * reply chunk */
> +#define NBD_CMD_FLAG_FAST_ZERO (1 << 4) /* fail if WRITE_ZEROES is not fast
> */
>
> /* Supported request types */
> enum {
> @@ -270,6 +273,7 @@ static inline bool nbd_reply_type_is_error(int type)
> #define NBD_EINVAL 22
> #define NBD_ENOSPC 28
> #define NBD_EOVERFLOW 75
> +#define NBD_ENOTSUP 95
> #define NBD_ESHUTDOWN 108
>
> /* Details collected by NBD_OPT_EXPORT_NAME and NBD_OPT_GO */
> diff --git a/nbd/common.c b/nbd/common.c
> index cc8b278e541d..ddfe7d118371 100644
> --- a/nbd/common.c
> +++ b/nbd/common.c
> @@ -201,6 +201,8 @@ const char *nbd_err_lookup(int err)
> return "ENOSPC";
> case NBD_EOVERFLOW:
> return "EOVERFLOW";
> + case NBD_ENOTSUP:
> + return "ENOTSUP";
> case NBD_ESHUTDOWN:
> return "ESHUTDOWN";
> default:
> @@ -231,6 +233,9 @@ int nbd_errno_to_system_errno(int err)
> case NBD_EOVERFLOW:
> ret = EOVERFLOW;
> break;
> + case NBD_ENOTSUP:
> + ret = ENOTSUP;
> + break;
> case NBD_ESHUTDOWN:
> ret = ESHUTDOWN;
> break;
> diff --git a/nbd/server.c b/nbd/server.c
> index b5577828aa44..981bc3cb1151 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -55,6 +55,8 @@ static int system_errno_to_nbd_errno(int err)
> return NBD_ENOSPC;
> case EOVERFLOW:
> return NBD_EOVERFLOW;
> + case ENOTSUP:
> + return NBD_ENOTSUP;
This may provoke returning NBD_ENOTSUP in other cases, not only new one we are
going to add.
> case ESHUTDOWN:
> return NBD_ESHUTDOWN;
> case EINVAL:
> diff --git a/qemu-nbd.c b/qemu-nbd.c
> index 079702bb837f..dce52f564b5a 100644
> --- a/qemu-nbd.c
> +++ b/qemu-nbd.c
> @@ -294,6 +294,7 @@ static int qemu_nbd_client_list(SocketAddress *saddr,
> QCryptoTLSCreds *tls,
> [NBD_FLAG_CAN_MULTI_CONN_BIT] = "multi",
> [NBD_FLAG_SEND_RESIZE_BIT] = "resize",
> [NBD_FLAG_SEND_CACHE_BIT] = "cache",
> + [NBD_FLAG_SEND_FAST_ZERO_BIT] = "fast-zero",
> };
>
> printf(" size: %" PRIu64 "\n", list[i].size);
>
--
Best regards,
Vladimir
